Since occlusion of coronary artery saphenous vein bypass grafts occurs and negates the benefits of surgery in up to 23% of patients, we have conducted experiments to elucidate the mechanisms of occlusion as well as experiments to determine the potential beneficial effects of antiplatelet drugs. Studies conducted during the first two years of this grant have indicated that administration of antiplatelet drugs decreases the incidence of early thrombosis and late intimal proliferation. These studies also suggest that the thrombotic process probably is initiated by damage occurring during harvesting of the vein graft. The most significant achievement during the past year was the demonstration that administration of antiplatelet drugs significantly (P less than 0.05) decreased the incidence of early thrombus formation in the coronary artery saphenous vein bypass graft. This documentation is of critical importance since it indicates a) that alterations of the vein wall occur during the operation and predispose to intraluminal thrombosis and b) that results of coronary artery surgery in humans may be improved with the use of antiplatelet drugs by reducing the incidence of early graft occlusion.